Apparatus for bending glass sheets are very well known in the art, and many variations of said apparatus exist in the marketplace. Basically an apparatus for bending glass sheets comprises a carrier ring mold which moves under a supported glass sheet, said glass sheet being supported by either air jets under the sheet, or by means of a ceramic perforated holder mold which holds the sheet by means of vacuum or by any combination of said supporting devices. The air jets or the vacuum is then terminated so that the glass drops onto the ring and bends under the bias of gravity in a manner that allows thin glass to be accurately bent. Subsequently the mold ring is moved from the furnace to a quench unit between upper and lower blastheads that temper the bent glass.
Thus, U.S. Pat. No. 4,282,026 describes an apparatus for bending and tempering glass sheets, wherein sheet glass is heated during conveyance on a conveyor within a furnace. A vacuum holder is positioned within the furnace housing above the conveyor and has a downwardly facing surface with spaced openings in which a vacuum is drawn to receive a glass sheet from the conveyor and support the sheet above the conveyor. A carrier mold ring moves under the supported glass and the vacuum is then terminated so the glass drops onto the ring and bends under the bias of gravity in a manner that allows thin glass to be accurately bent. Subsequently the mold ring is moved from the furnace to a quench unit that tempers the bent glass.
U.S. Pat. No. 4,386,952 describes a glass sheet bending system which utilizes gas jets for the bending operation and which comprises a compressed gas bending unit located above a horizontal conveyor on which glass sheets are heated within a furnace. A downwardly facing curved surface of a holder above the conveyor receives a heated glass sheet for bending. Compressed gas fed through outlets of the bending unit provides inclined gas jets directed in a generally perpendicular relationship to the holder surface with a sufficient intensity to bend the glass sheet on the holder to the curved shape of its surface. A blow-up unit and a vacuum drawing unit for the holder and a vertically operable actuator for the holder preferably cooperate with the bending unit. A curved mold is moved to below the holder to receive the bent glass sheet and further bending of the glass sheet preferably takes place on the mold under the operation of gravity. The system also includes a quench unit to which the mold moves the bent glass sheet for tempering.
U.S. Pat. No. 4,437,871 describes an apparatus for bending glass sheets which is very similar to the apparatus of U.S. Pat. No. 4,282,026, with an improved vacuum support of the glass sheets, by providing a greater vacuum to initially support the glass and a lesser vacuum to subsequently prevent glass deformation at the spaced openings of the holder. Sensors are provided for sensing the glass position along the conveyor and operation of a locator cooperatively provide accurate positioning of the glass on the holder surface without requiring the conveyor to be stopped prior to the holder operation.
U.S. Pat. No. 4,437,872 describes an apparatus which is identical to that of U.S. Pat. No. 4,437,871, with improved conveyance system.
U.S. Pat. No. 4,517,001, in turn, describes, an apparatus for bending glass sheets which operates under the same principle mentioned for the above identified patents, and which also uses a mold ring positioned within a furnace to deposit thereon the glass sheet transported by the vacuum holder, after removing the vacuum so that the glass sheet bends under the force of gravity on said mold ring.
None of the above described prior art glass sheet bending apparatus, however, are capable of bending glass sheets which require a deep or abrupt curvature, along the periphery of the sheet, such as the curvature needed for modern automotive glasses, which are being increasingly required by the automotive industry throughout the world to be installed in modern cars.
Although some efforts in this respect have been made by workers in the past, none of said efforts has resulted in an apparatus, of very economical construction and easy operation, which may obtain the curvatures mentioned above, which are not obtainable through the use of mere gravity ring molds as those utilized in almost all the apparatus of the prior art described above.
One of said efforts, for instance, is represented by the apparatus for bending glass sheets described in U.S. Pat. No. 4,204,854, which describes an apparatus for bending heated sheets of glass transported generally horizontally on a conveyor within a furnace heating chamber, and which incorporates a holder located above the conveyor in a spaced relationship such that a heated sheet of glass can be transported under the holder. Gas such as air is blown upwardly from below the conveyor against the heated sheet of glass such that the sheet is moved upwardly into engagement with the holder. A mold ring is then movable under the holder to receive the glass sheet for bending. Vertical movement of the holder facilitates the lifting and also enables the curved surface and curved ring embodiments of the holder to bend the lifted glass sheet between the holder and the mold ring. This provides a press forming of glass sheet between the holder and the ring mold, whereby abrupt changes in curvature may be effected on the glass sheet, in order to match the design curvature. However, this apparatus not only is very expensive, but also has the disadvantage that the entire surface of the holder is pressing against the glass sheet on the mold ring, whereby at least slight marring of the glass sheet cannot be avoided.
U.S. Pat. No. 4,356,018, in turn, describes an apparatus for deep bending of glass sheets, which provides for the minimal sliding of the glass sheet with respect to a curved bending mold utilized, as well as insures accurate positioning of the glass sheet on the mold for bending to the desired shape and permits relatively abrupt end bends to be performed. In this apparatus, a heated glass sheet is initially supported against a downwardly facing surface of a holder above the curved bending mold which has an upwardly concave shape. An upward gas flow from a gas supply unit at a central portion of the glass sheet is supplied and continued as opposite extremities of the glass sheet are released and dropped downwardly onto the mold. Thereafter, termination of the upward gas flow from the gas supply unit releases the central portion of the glass sheet for bending on the mold. After bending, the mold is moved to a quench unit for tempering of the bent glass sheet. Although this apparatus, by firstly releasing the peripheral sections of the glass sheets to be deposited on the mold ring, allowing more time for the gravity bending of the glass sheet at the extremities of the mold ring, maintains the central portion of the glass sheet against the surface of the holder during a relatively longer time, and thusly provides a deep deformation, which is opposite to the desired deformation of the center of the glass sheet, and which when the center of the glass sheet is released, may cause wrinkles and other defects, on the surface of the glass sheet, whereby although this apparatus is perfectly capable of obtaining deep bends particularly on the periphery of the glass sheet, it also produces a percentage of reject bent glass sheets, due to the above mentioned defect and, in order to avoid this possibility, requires a very accurate and strict control of the timing of the operation (and a very precise and costly tooling).
U.S. Pat. No. 4,514,208, on the other hand, also describes an apparatus for use in bending heated sheets of glass transported generally horizontally on a conveyor within a furnace heating chamber, and includes a holder and a counterbalanced bending member, both of which are located above the conveyor in a spaced relationship such that a heated sheet of glass can be transported under the holder. The holder includes a curved, downwardly facing surface with spaced openings in which vacuum is drawn to receive the glass sheet from the conveyor. Gas, such as air, is blown upwardly from below the conveyor against the heated sheet of glass such that the sheet is moved upwardly and into engagement with the curved surface of the holder. The bending member then moves downwardly below the holder surface and thereafter upwardly against the heated sheet of glass to provide bending thereof to the curved shape of the holder surface. The bending member then moves back to its home position above the holder surface and a carrier mold ring moves under the supported glass, the vacuum is then terminated so the glass drops onto the ring and bends under the bias of gravity in a manner that allows the glass to be further bent. Although this apparatus is also capable of producing sharp bends on any area of the glass sheet, it also has the defect already described in connection with U.S. Pat. No. 4,204,854 of having the surface of the sheet pressed between two members, which may produce frequent marring of the glass sheet with the consequent decrease in quality of the glass sheet, to prevent this a very accurate process and expensive tooling must be made considering that said bent glass sheet may be used for the manufacture automotive glasses which must be absolutely clear.
Finally, U.S. Pat. No. 4,609,391, describes an apparatus for forming glass sheets in an accurate manner, to a deep, abrupt or complex curvature by utilizing a first curved mold that initially forms the glass sheet at a first forming station preferably by the operation of gravity. The initially formed glass sheet is moved horizontally preferably by movement on the first curved mold to a second forming station. A second curved mold of the second forming station engages the initially formed glass sheet to provide accurate forming preferably by downward movement of the second curved mold that provides the engagement thereof with the glass sheet. Although this apparatus may also provide sharp bends on any area of the glass sheet and particularly on the periphery thereof, it requires a very complicated system of transportation of the glass sheet, because firstly the glass sheet is transported by a conveyor within the furnace or lehr, then the glass sheet is deposited on the first mold and is thereafter transported thereby, with the consequent intricacy of the mechanisms necessary to effect said movements, and lastly the second or bending mold must be lifted and the glass sheet released thereby on a transfer reciprocatable conveyor to extract the sheet from the lehr. This, without avoiding the possibility of severe marring of the surface of the glass sheet, also implies the provision of very complicated and costly mechanisms for conveying the glass sheet along the bending and the heating apparatus, which results in a very costly operation.